ABSTRACT
For over a decade hollow-core fibers have been used in optical gas sensors in the role of gas cells. However, very few examples of actual real-life applications of those sensors have been demonstrated so far. In this paper, we present a highly-sensitive hollow-core fiber based methane sensor. Mid-infrared distributed feedback interband cascade laser operating near 3.27â µm is used to detect gas inside anti-resonant hollow-core fiber. R(3) line near 3057.71â cm-1 located in ν3 band of methane is targeted. Compact, lens-free optical setup with an all-silica negative curvature hollow-core fiber as the gas cell is demonstrated. Using wavelength modulation spectroscopy and 7.5-m-long fiber the detection limit as low as 1.54 ppbv (at 20 s) is obtained. The demonstrated system is applied for a week-long continuous monitoring of ambient methane and water vapor in atmospheric air at ground level. Diurnal cycles in methane concentrations are observed, what proves the sensor's usability in environmental monitoring.
ABSTRACT
We present laser-based methane detection near 1651 nm inside an antiresonant hollow-core fiber (HCF) using photothermal spectroscopy (PTS). A bismuth-doped fiber amplifier capable of delivering up to more than 160 mW at 1651 nm is used to boost the PTS signal amplitude. The design of the system is described, and the impact of various experimental parameters (such as pump source modulation frequency, modulation amplitude, and optical power) on signal amplitude and signal-to-noise ratio is analyzed. Comparison with similar PTS/HCF-based systems is presented. With 1.3 m long HCF and a fiber amplifier for signal enhancement, this technique is capable of detecting methane at single parts-per-million levels, which makes this robust in-fiber sensing approach promising also for industrial applications such as, e.g., natural gas leak detection.
ABSTRACT
In this paper, we report the performance of a bismuth-doped fiber amplifier at 1687 nm. This wavelength region is particularly interesting for laser-based spectroscopy and trace gas detection. The active bismuth-doped fiber is pumped at 1550 nm. With less than 10 mW of the seed power, more than 100 mW is obtained at the amplifier's output. We also investigate the signal at the output when a wavelength-modulated seed source is used, and present wavelength modulation spectroscopy of methane transition near 1687 nm. A significant baseline is observed in the spectra recorded when the fiber amplifier is used. The origin of this unwanted background signal is discussed and methods for its suppression are demonstrated.
ABSTRACT
In this paper we report a mid-infrared sensor based on an anti-resonant hollow core fiber. A quantum cascade laser operating around 4.53 µm is used to target one of the strongest transition of nitrous oxide near 2203.7 cm-1. The system provides 1-second minimum detection limit at single parts-per-billion level using 3.2-m-long fiber with the response time of less than 30 seconds. Presented sensing approach shows a good perspective for compact and sensitive mid-infrared fiber-based spectrometers.
ABSTRACT
In this paper, we present a laser-based sensing inside anti-resonant hollow core fiber. A distributed feedback laser diode operating near 2004 nm and a 1.35-m-long silica-based fiber are used to demonstrate carbon dioxide detection with sensitivity down to ~5 ppmv. Gas exchange time as low as 5 seconds is obtained. This performance was achieved in a very simple optical configuration, without any mirrors or lenses in the setup.